The invention relates to electronic musical instruments, and more particularly to electronic musical instruments provided with a plurality of tone production channels less than the number of keys.
In an electronic musical instrument having an upper keyboard generally often used for melody performance and a lower keyboard generally often used for accompaniment performance, the tones produced by the upper keyboard and lower keyboard are usually different tone colors from each other, with the result that a plurality of the upper keyboard production channels and a plurality of the lower keyboard production channels should be independently constructed. One of the known electronic musical instruments of this type is disclosed in U.S. Pat. No. 4,192,211. The number of production channels provided for the upper keyboard and that for the lower keyboard shall be equal the number of the simultaneous maximum tones to be produced, e.g., around 10, since there are cases when performance is made by both hands using only the upper keyboard, or when performance is made by both hands using only the lower keyboard. However, in general practice, melody performance is made by one hand (right hand) using the upper keyboard and accompaniment performance is made by the other hand (left hand) using the lower keyboard. In this case, both the number of the upper keyboard production channels and the number of the lower keyboard production channels are considerably smaller than the total number of channels (around 1 to 3 channels), and many production channels remain unused.
On the other hand, in an electronic musical instrument which has a single keyboard, it is practiced that the keyboard is divided into the higher tone key range for the melody performance and the lower tone key range for the accompaniment performance, in which tones of different tone colors are produced. In this type of electronic musical instruments, a plurality of tone production channels are provided respectively correspondingly to the melody and accompaniment, and the number of channels for each thereof is not usually so large. This is to prevent wastefulness caused by the presence of unused production channels and to reduce the production cost. However, this involves an inconvenience that when a free performance is attempted, e.g., when multiple tones are to be performed simultaneously by the melody tone color, departing from the limit of expected form of performance, e.g., one tone for melody and simultaneous 3 tones for accompaniment, the performance cannot be made by the electronic musical instrument having only a limited number of melody production channels.
To solve the above problem, an electronic musical instrument was proposed by A. Nakada et al in the preceding application U.S. Ser. No. 182,464 "Electronic Musical Instrument with Plural Tone Production Channels" dated Aug. 28, 1980 (assigned to the same assignee as the present case), in which the relationship between the production channel and key range (or key board) was not fixed but made variable according to the performance mode, i.e., all production channels could be set to produce melody tone through the whole keyboard or the production channels could be used divided between the melody tone (specific key range tone) and accompaniment tone (different key range tone). Since the depressed key information indicating the depressed key is a multiple bit key code, the circuit processing the depressed key information tends to be complex. For example, when tones of each key range of a single keyboard are to be assigned to a production channel group dividing, the key code indicating the depressed key should be fed to the comparator circuit or ROM (read only memory) key detector, and the key range should be detected based on the value of the key code. Accordingly, relatively complex circuits, such as the comparting circuit and ROM, are required. In addition, further data such as automatic bass tone should be generated based on the depressed key information depending on the selected performance mode. In such case, the key code for the automatic bass tone is formed based on the arithmetic operation such as addition of subordinate note calculation data to the key code of root note. Accordingly, the arithmetic (operation) circuit of plural bit data is essential thereby making the circuit composition complex.